I think you missed my point...The fact that you have two different size drives and different format the question in my mind is how can parity be valid when I swap out a 2TB RFS drive with 4TB xfs drive. I know it works out now but at the time it was a strech to comprehend this.
From a parity standpoint, size doesn't matter, format doesn't matter, data doesn't matter, nothing matters but the bits on every drive, whether you are using them or not. From a parity standpoint, drives are all the same size, exactly as big as the parity drive. They just have zeroes past the end of the physical drive.
Here are links explaining parity (the second has more links):
Parity-Protected Array, from the Manual
How does parity work?

Not related, but you have IDE emulation turned on for your onboard SATA drives. When you next boot, go into the BIOS settings and look for the SATA mode, and change it to a native SATA mode, preferably AHCI if available, anything but IDE emulation mode. It should be slightly faster, and a little safer.
You had your first segfault on March 16 at 2:05am, then again March 24 at 2:03am, then on March 27 around 7:30pm, then the last on March 30 at 2:05am. All were associated with Plex Media Scanner. A couple of them mention libjemalloc, but I'm not sure that matters because after the first segfault, the program may not have been running correctly, and that was on March 16. When these are reported, you should reboot when next convenient. Don't keep running just because it feels like nothing's wrong.
The 2 main causes for segfaults are RAM faults and dependency issues, then well after those, program bugs. In this case, I think it's a dependency issue, and for that you'll need PhAzE to take a look, when he has time. These are rarely easy to figure out.
There is a clear association with the time, a little after 2am, so you might look into what happens around then.

Ah, good point! Can't have everything. But where I'm running into this most is the wiki procedure for converting drives to XFS, and Parity2 is invalid any way, because of all the drive swapping and reassignment.

Done.
That's why my very first step is to recommend a parity check, so that you know there are no drive problems to take care of, and that parity is good. There's no reason it should not stay good throughout.
Keep it coming!
I have also added a summary of the method to begin it with, and a new Method section, with the various factors that are involved and comparative verbiage between the different methods. The methods are only summarized. Will it be helpful? Probably not, so many more words added...

That should be : rsync -avPX /mnt/disk3/ /mnt/disk7
Note the slash after the 3. Without that slash, you will end up with a disk3 folder on Disk 7 (/mnt/disk7/disk3). With the slash added, you will end up with the entire contents of Disk 3 on Disk 7, and no disk3 folder.

tunetyme, would you mind checking the change I've made? Here's the old Step 16:
You should see all array disks with a blue icon, a warning that the parity disk will be erased, and a check box for Parity is already valid; IMPORTANT! click the check box, make sure it's checked to indicate that Parity is already valid or your Parity disk will be rebuilt! then click the Start button to start the array; it should start up without issue and look almost identical to what it looked like before the swap, with no parity check needed; however the XFS disk is now online and its files are now being shared as they normally would; check it all if you are in doubt
And here's the new version:
You should see all array disks with blue icons, and a warning (All data on the parity drive will be erased when array is started), and a check box for Parity is already valid. VERY IMPORTANT! Click the check box! Make sure that it's checked to indicate that Parity is already valid or your Parity disk will be rebuilt! Then click the Start button to start the array. It should start up without issue (and without erasing and rebuilding parity), and look almost identical to what it looked like before the swap, with no parity check needed. However the XFS disk is now online and its files are now being shared as they normally would. Check it all if you are in doubt.
Before you click the Start button, you may still see the warning about the parity drive being erased, but if you have put a check mark in the checkbox for Parity is already valid, then the parity drive will NOT be erased or touched. It is considered to be already fully valid.

Howdy c3! We meet again!
If that was all the paper boy wanted to do, what you presented above, there probably wouldn't be much of an issue. But the problem is that the paper boy doesn't want to just toss the paper, and he doesn't want to just come to the door and knock and seek permission. The paperboy wants to walk right in with a huge notebook and wander around the rooms. He looks in on Father, and writes down that he's looking at a replacement for the TV. He looks in on Mother and writes down she's checking on shoes. He checks on big sister, and notes she's reading up on STD's. He checks up on the son, and notes he's reading about bomb making (I threw that in for a curve ball). Then he leaves and walks into the neighbor's house and repeats. At the end of the day, he goes online and advertises that he has some huge notebooks for sale!

Paul, I take back much of what I said - I never saw that comment by JonP, or any similar comments that there was *ANY* Ryzen support available yet, at all! And I also was completely unaware that any Ryzen support had been added to 4.9.10. ALL of the comments related to that seemed to be that they were waiting for 4.10 or 4.11. I do apologize for that.
But aren't there comments that LimeTech wasn't completely successful yet? I take that to mean they aren't done making appropriate changes. Also, have you seen any info on whether KVM/QEMU and related are updated for Ryzen yet? That's fairly important I think.
There is certainly a lot of interest in this thread, probably a lot more than anyone here realizes. And Paul, while we can't possibly pay you for the investigative work you have done, it is invaluable, has been and will be very helpful!

Perhaps deprecate it first, for a few versions. Stick a " [Not recommended] " next to it, in the appropriate places. This would help Tom evaluate the feedback, how upset some might be without it. Hopefully, there's no reaction at all.

It will need Tom ( @limetech ) or other AD experienced people to see (I'm not one of them).
First try was at 7:01, unsuccessful, and all attempts for awhile returned "exit status: 1". Finally at 01:20:09, there was progress, although still with errors.
Once you tried to turn off AD, something was wrong with avahidaemon, which is why you had to reboot.

It wouldn't be applicable for a new system, so perhaps shouldn't even appear then. But take a look at my newest suggestion, link below, makes the "parity is valid" checkbox almost obsolete, almost not needed any more. It lets the system decide when parity is valid or not. I think I'd still want it available, for the odd case where you reconstruct an array that used-to-be? Like a lost super.dat? Like a v4.7 array being converted, in a clean install?
Allow drive reassignments without requiring New Config